U.S Pat. No. 2,559,227 to RIEBER discloses pressure wave generation by electric discharge between two electrodes disposed at the first focus of a truncated ellipsoid so as to destroy a target disposed at the second focus of the ellipsoid. The pressure wave is created by the electric arc generated between the electrodes which suddenly vaporizes part of the liquid, causing formation of bubbles in the coupling liquid in which the electrodes are immersed. This liquid is constituted in particular by water. In addition, the gases which are dissolved in the liquid are for example nitrogen, oxygen, carbon dioxide gas, in particular when it is question of water. Likewise, a small part of water is also dissociated electrolytically.
Now, for optimum transmission of the pressure waves, it is necessary that the coupling liquid transmitting the pressure waves be bereft of bubbles of gas.
U.S. Pat. No. 4,530,358 proposes to circulate the coupling liquid between the pressure wave generation chamber and a recycling circuit in which at least one gas bubble eliminating device is provided. One of these means consists in particular in a vacuum degassing means (col. 2, lines 43-45). It is also provided to tilt the pressure wave generating and focussing chamber (col. 2, lines 46-53). In an embodiment forming the subject matter of FIG. 2 of U.S. Pat. No. 4,530,458, the liquid communicates freely with the atmosphere and, in that case, a deflecting means is provided, deviating the gas bubbles from the zone of the body of a patient having to receive the pressure waves.
It will be readily appreciated that these means are complicated and expensive, whilst the use of a deflecting device interposed in the path of the pressure waves is not practicable, as this deflecting element constitutes a physical obstacle interrupting the passage of the pressure waves.
It is therefore an object of the present invention to solve the novel technical problem of providing a solution for effecting simple and efficient degassing of a coupling liquid of a pressure wave generating apparatus, ensuring virtually perfect safety and reproducibility.
This novel technical problem is solved for the first time by the present invention in simple, reliable, inexpensive manner, usable on an industrial scale.